Method of establishing logical connections in a synchronous digital communications network, as well as network elements and management system

ABSTRACT

A method of establishing logical connections in a synchronous communications network (SDH) comprising a plurality of at least partially interconnected network elements (NE 1 , NEn; CC 1 -CC 3 ) and designed for the transmission of data packets containing a destination address involves monitoring destination addresses of the data packets to be transmitted, determining the traffic volume between the individual network elements (NE 1 , NEn; CC 1 -CC 3 ) with the aid of the destination addresses, and determining an optimized configuration of logical connections based on the traffic volume and existing logical connections. In this manner, the communications network is adapted to the current traffic situation, and the transmission capacities of the network are utilized in the best possible manner. The monitoring is advantageously done in at least part of the network elements, while the determination of the traffic volume and the optimized configuration is performed by a central management system (TMN).

[0001] This invention relates to a method of establishing logicalconnections in a synchronous digital communications network as claimedin claim 1, to a network element for a synchronous digitalcommunications network as claimed in claim 9, and to a management systemas claimed in claim 11.

[0002] Data packets, which originate, for example, from local areanetworks, are transmitted through data networks to respectiveaddressees. Such data packets originate particularly from Internetapplications, are structured in accordance with the Internet protocol(IP), and have a source address and a destination address. Astransmission media (OSI Layer 1) for long-haul data communicationsnetworks, synchronous digital networks based on the SDH or SONETstandards and recommendations are used (SDH=Synchronous DigitalHierarchy, SONET=Synchronous Optical Network). This is stated, forexample, in RFC 1619 (W. Simpson, Request for Comments 1619, InternetEngineering Task Force, Network Working Group, May 1994), which proposesto place data packets to be transferred over point-to-point linksdirectly in synchronous transport modules (STM-N) of SDH or synchronoustransport signals (STS-N) of SONET.

[0003] In synchronous digital communications networks, virtual, i.e.,logical, connections can be switched between elements of the network.This is done manually with the aid of a management system. The switchedlogical connections are then used by routers of different data networks,which provide the gateways to the synchronous digital communicationsnetwork, to transmit data packets.

[0004] Since applications of the Internet, in particular, produce widelytime-varying data quantities (between 0 b/s and a few Mb/s) which haveto be transmitted over the synchronous digital communications network inthe form of IP data packets, the prior art has the disadvantage thateither large transmission capacities have to be kept available in thecommunications network, which then remain unused most of the time, orthat bottlenecks occur if several users want to send large amounts ofdata simultaneously.

[0005] In another concept, IP packets are first placed in ATM cells andthen transmitted over virtual channel connections through a synchronousdigital communications network (SDH or SONET). In an article publishedby Ipsilon Networks (“IP Switching: The Intelligence of Routing, thePerformance of Switching”, Ipsilon Technical White Paper on IPSwitching, February 1996, retrievable in the Internet athttp://www.ipsilon.com/productinfo/wp-ipswitch.html), a device (IPSwitch) is presented which combines the functions of an IP router and anATM switch. This device is capable of identifying longer-durationsequences of data packets having the same source and destinationaddresses, so-called flows, by means of an address monitor, and toswitch suitable connections for these flows in the hardware. Thisincreases the throughput of data packets through the IP switch andshortens the mean switching time. This, too, has the disadvantage thatonly predetermined logical connections can be used, which are eitherunderdimensioned or overdimensioned, depending on the current payload.

[0006] It is an object of the invention to provide a method whereby asynchronous digital communications network can be better adapted totime-varying data traffic. Further objects of the invention are toprovide a network element and a management system for a synchronousdigital communications network which are suited for carrying out themethod.

[0007] The objects are attained by the features of claims 1, 9, and 11,respectively.

[0008] One advantage of the invention is that transmission capacitiescan be better utilized for the transmission of data packets and that theaverage transmission rate is higher than in the prior art. Otheradvantages are that commercially available IP routers can be used, andthat no changes to the equipment of a user wishing to transmit datapackets over the communications network are necessary.

[0009] In a preferred embodiment of the invention, source-addressmonitoring is additionally performed. This makes it possible todetermine charges for transmitted data packets.

[0010] In another preferred embodiment of the invention, data packetswith predetermined source or destination addresses, e.g., all datapackets from or for an individual, predetermined user, are given ahigher priority during transmission.

[0011] One embodiment of the invention will now be described withreference to the accompanying drawing, in which:

[0012]FIG. 1 shows two local area networks (LANs) interconnected by asynchronous digital communications network;

[0013]FIG. 2a shows a configuration of a communications network for highdata traffic between adjacent users; and

[0014]FIG. 2b shows a configuration of a communications network for highdata traffic between users located remote from each other.

[0015] Referring to FIG. 1, there are shown two local data networksLAN1, LAN2 which are interconnected by a synchronous digitalcommunications network SDH and can exchange data packets via thisnetwork. The gateways from the local area networks to the communicationsnetwork SDH are provided by routers RTR1, RTR2. Each of the latter isconnected to a network element NE1, NE2 of the network SDH. Betweenthese two network elements NE1, NE2, a logical connection exists throughthe network SDH over which the data packets to be transmitted aretransported. If data packets are to be transmitted from the first localarea network LAN1 to the second local area network LAN2, they are placed(“packetized”) in synchronous transport modules or subunits of suchsynchronous transport modules, so-called virtual containers VC-N (inSDH) or virtual tributaries VT (in SONET), in the first network elementNE1, and transmitted to the second network element NE2, where they areunpacketized and passed to the second router RTR2. Besides SDH and SONETsystems, plesiochronous digital hierarchy (PDH) transmission systemsmust be regarded as synchronous digital networks in the sense of theinvention.

[0016] A logical connection (frequently also referred to as a virtualconnection) is formed as two network elements periodically exchangesubunits of synchronous transport modules, with the subunits beingswitched through other, intermediate network elements of thecommunications network SDH without being repacketized Virtualconnections are established by a central network management system ofthe synchronous digital network SDH and have a fixed transmissioncapacity, i.e., they are permanent virtual connections.

[0017] A fundamental idea of the invention is to monitor in thecommunications network the destination addresses of the data packets tobe transported, to determine therefrom the traffic volume between theindividual network elements of the communications network, and, based onthe traffic volume, to determine an optimized configuration of logicalconnections which is used to update the network. The network is thusadapted to the current traffic volume, and the transmission capacitiesof the network are utilized in the best possible manner. This approachis particularly suitable for IP data packets of Internet applications,but it is also applicable to data packets structured according to otherprotocols, preferably of OSI Layer 3, such as the IPX procotol of NovellInc.

[0018] Particularly advantageously, the monitoring of the destinationaddresses is performed in at least part of the network elements of thesynchronous communications network. To this end, the network elementsinclude means for monitoring the destination addresses, e.g., an IPaddress monitor. Alternatively, the use of a separate address monitorlooped into a connection path of the network is possible. In anotherpreferred embodiment, the determination of the traffic volume and thedetermination of an optimized configuration are performed in a centralmanagement system of the communications network. The network elementsnotify the management system of results of the monitoring of thedestination addresses, from which the management system can determinethe traffic volume. Via the interfaces (e.g., a Q interface) providingthe connection between the management system and the network elements,instructions are then transmitted to the network elements relating tological connections to be switched by the network elements. In thismanner, the management system establishes the logical connections in thenetwork in accordance with the optimized configuration.

[0019] Advantageously, an optimized configuration is determinedperiodically and the logical connections are updated periodically. Thismay be done, for example, every day, every hour, or every minute(pseudo-online), depending on the application.

[0020]FIGS. 2a and 2 b show three network elements CC1-CC3 of thesynchronous digital communications network in one embodiment of theinvention, the first and second network elements and the second andthird network elements being physically interconnected by, e.g., opticalfibers or coaxial cables, but the physical connections are not shown inthe figure. The connections shown are logical connections. Each of thethree network elements is connected via an interface to a centralmanagement system TMN. From the latter they can receive instructions asto which logical connections have to be switched internally. Connectedto the three network elements CC1-CC3 are routers RTR1-RTR3,respectively, which provide the gateways from respective local areanetworks (not shown) to the communications network. The router routesdata packets from the local area network connected to it which aredestined for an addressee in another local area network to the networkelements connected to it, where they are packetized in subunits ofsynchronous transport modules and transmitted over one of the logicalconnections to a further network element.

[0021] According to the invention, the destination address of each datapacket is monitored in the sending network element prior to thepacketizing of the data packet. The result of this monitoring is passedin the form of a message MTL to the central management system TMN. It isalso possible to combine the results of the monitoring of two or moredata packets to be transmitted and send them as one message MTL to themanagement system TMN.

[0022] In the configuration shown in FIG. 2a, there are two logicalconnections between every two adjacent network elements, while there isno logical connection between the two remote network elements CC1 andCC3. This configuration is suitable for high data traffic volumesbetween the adjacent network elements CC1, CC2 and CC2, CC3. Trafficbetween remote network elements, i.e., data packets to be sent from CC1to CC3, must be depacketized in CC2, passed to the associated routerRTR2, checked there, and returned to CC2, from where they can then betransmitted to CC3.

[0023] In all three network elements, the destination addresses of alldata packets to be transmitted by the respective network element aremonitored. The results of the monitoring are communicated as messagesMTL to the central management system TMN. The management system TMNdetermines the current traffic volume from these messages, and from thecurrent traffic volume, it determines an optimized configuration withwhich the logical connections in the communications network are thenupdated. To do this, the management system sends to the network elementsinstructions ANW relating to the logical connections to be switched byeach network element.

[0024] If increased data traffic occurs between the remote networkelements CC1 and CC3, the management system TMN will determine that alogical connection between the network elements CC1 and CC3 is necessaryfor an optimized configuration, and will send to the network elementsCC1-CC3 an instruction ANW to switch the corresponding connection, i.e.,to switch a virtual container representative of the logical connectionfrom the first network element CC1 through the second network elementCC2 to the third network element CC3.

[0025] The optimized configuration for data traffic between the remotenetwork elements CC1 and CC3 is shown in FIG. 2b. The optimizationincreases the throughput of IP packets and reduces the transmissiondelays through the communications network.

[0026] From the IP routers, such an optimization of the communicationsnetwork would not be possible, since the IP routers have no knowledge ofthe topology of the network. By contrast, newly established or no longerexisting logical connections can be automatically identified and used orcircumvented by the routers, for example by the polling method.Therefore, after short identification times, the transmission networkdynamically optimized by the method according to the invention can beused by routers for routing.

[0027] Another advantage is that at the gateways to the communicationsnetwork, commercially available routers with commonly used interfacescan be employed, such as routers with E1, E3, E4, T1, T3, DS1, DS3,OC-n, or STM-n interfaces. The user equipment need not be modified,either.

[0028] Advantageously, the monitoring of the destination addresses isperformed in crossconnectors which are designed to switch logicalconnections in a synchronous digital communications network.

[0029] Instead of providing network elements with IP monitors formonitoring the destination addresses, the routers may be provided withan interface to the central management system for informing themanagement about the current traffic situation.

[0030] A further development of the invention consists of monitoring notonly the destination addresses of the data packets, but also the sourceaddresses. In this manner, charging for the transmission of data packetscan be implemented, for example by simply counting the transmitted datapackets for each source.

[0031] According to another development of the invention, data packetsselected according to predetermined criteria are given preferentialtreatment, i.e., higher priority. Such criteria may be particularly thesource or destination addresses of the data packets. In this manner, amore reliable and faster data link can be made available to selectedusers, for example to users paying a higher tariff.

[0032] According to a further development of the invention, experiencegained in cyclically occurring traffic situations are taken into accountin determining the optimized configuration. Such experience may begained, for example, by statistical eveluation over prolonged periods oftime or from the typical behavior of individual users. For instance, itmay be known from observations that every Sunday night, two usersexchange data with a high data traffic volume. The transmission capacityregularly required for this transaction is then automatically madeavailable in the form of a logical connection already shortly before thebeginning of the data transfer and the connection is automaticallyreleased after termination of the transaction.

1. A method of establishing logical connections in a synchronous digitalcommunications network (SDH) comprising a plurality of at leastpartially interconnected network elements (NE1, NEn; CC1-CC3) designedfor the transmission of data packets each containing a destinationaddress, said method comprising the steps of: monitoring the destinationaddresses of the data packets to be transmitted; determining a currenttraffic volume between the individual network elements (NE1, NEn;CC1-CC3) with the aid of the destination addresses; determining anoptimized configuration of logical connections based on the trafficevolume and existing logical connections; and updating the logicalconnections in the synchronous digital communications network (SDH) withthe optimized configuration.
 2. A method as claimed in claim 1 whereinthe determination of the optimized configuration and the updating of thelogical connections are performed periodically.
 3. A method as claimedin claim 1 wherein the the data packets are packets structured inaccordance with the Internet protocol.
 4. A method as claimed in claim 1wherein the monitoring of the destination addresses is performed in atleast part of the network elements (NE1, NEn; CC1-CC3) of thesynchronous digital communications network.
 5. A method as claimed inclaim 1 wherein the determination of the traffic volume and thedetermination of an optimized configuration are made by a centralmanagement system (TMN) of the synchronous digital communicationsnetwork (SDH).
 6. A method as claimed in claim 1 wherein in addition,the source addresses are monitored and a charge for transmitted datapackets is determined therefrom.
 7. A method as claimed in claim 1 or 6wherein data packets with predetermined source or destination addressesare given a higher priority during transmission.
 8. A method as claimedin claim 1 wherein the determination of the optimized configuration isalso based on experience gained in cyclically occurring trafficsituations.
 9. A network element (NE1, NEn; CC1-CC3) for a synchronousdigital communications network (SDH) comprising a plurality of at leastpartially interconnected network elements and designed for thetransmission of data packets, said network elements (NE1, NEn; CC1-CC3)comprising: means for monitoring destination addresses of the datapackets to be transmitted; and an interface to a central managementsystem (TMN) for sending messages (MTL) containing the destinationaddresses of the data packets to be transmitted and for receivinginstructions (ANW) relating to logical connections to be switched, thecentral management system (TMN) being provided for establishing thelogical connections in the communications network (SDH).
 10. A networkelement as claimed in claim 9 which is a crossconnector (CC1-CC3).
 11. Amanagement system (TMN) for a synchronous digital communications network(SDH) comprising a plurality of at least partially interconnectednetwork elements (NE1, NEn; CC1-CC3) and designed for the transmissionof data packets, said management system (TMN) comprising: interfaces tothe network elements (NE1, NEn; CC1-CC3) of the synchronous digitalcommunications network (SDH) for receiving messages (MTL) containingdestination addresses of the data packets to be transmitted and forsending to the network elements (NE1, NEn; CC1-CC3) instructions (ANW)relating to logical connections to be switched; means for determining acurrent traffic volume between the network elements based on themessages (MTL) containing the destination addresses of the data packetsto be transmitted; means for determining an optimized configuration oflogical connections between the network elements (NE1, NEn; CC1-CC3)based on the existing logical connections and the traffic volume; andmeans for sending to the network elements (NE1, NEn; CC1-CC3)instructions (ANW) relating to the logical connections to be switched inaccordance with the optimized configuration.